Communication device and method, and program

ABSTRACT

The present invention relates to a device and a method for communication, and a program that make it possible to provide a communication environment not limited by a use environment. An electrode controlling unit in a transmitting device checks a state of capacitive coupling of each of an electrode and an electrode in an electrode unit with surroundings, controls connection of each electrode to a transmitting unit according to a result of the check, and makes the electrode and the electrode function as a transmission signal electrode or a transmission reference electrode, the transmission signal electrode and the transmission reference electrode being different from each other. The transmitting unit connects the electrode and the electrode to an amplifying unit under control of the electrode controlling unit, and transmits a signal to a communication medium via one of the electrodes. The present invention is applicable to communication systems.

TECHNICAL FIELD

The present invention relates to a device and a method forcommunication, and a program, and particularly to a device and a methodfor communication, and a program that make communication possible in thecommunication device having at least two electrodes irrespective ofphysical positional relation between a user of the communication deviceand the communication device.

BACKGROUND ART

Conventionally, in a communication system including a transmittingdevice, a communication medium, and a receiving device, a physicalcommunication signal transmitting path for transmitting a communicationsignal and a physical reference point path different from thecommunication signal transmitting path, the reference point path beingto share a reference point for determining a difference in level of thecommunication signal between the transmitting device and the receivingdevice, are provided to perform communication (see for example PatentDocument 1 or Patent Document 2).

For example, Patent Document 1 and Patent Document 2 describecommunication techniques using a human body as a communication medium.In both methods, a human body is used as a first communication path, anddirect capacitive coupling between electrodes in a ground or a space isprovided as a second communication path, so that an entire communicationpath formed by the first communication path and the second communicationpath forms a closed circuit.

[Patent Document 1]

-   Japanese Patent Laid-Open No. Hei 10-229357

[Patent Document 2]

-   JP-A-Hei 11-509380

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

However, in such a communication system, two communication paths, thatis, the communication signal transmitting path and the reference pointpath (the first communication path and the second communication path)need to be provided as a closed circuit between the transmitting deviceand the receiving device. Since the two paths are different paths,making the two paths stably coexist with each other may limit a useenvironment for communication.

For example, the strength of capacitive coupling between thetransmitting device and the receiving device in the reference point pathdepends on a distance between the devices, and therefore the stabilityof the path differs depending on the distance. That is, in this case,there is a fear of the stability of communication depending on thedistance of the reference point path between the transmitting device andthe receiving device. In addition, there is a fear of the stability ofcommunication being changed by the presence of a shielding object or thelike between the transmitting device and the receiving device. Further,for example, when a ground is set as a reference point, and thetransmitting device and the receiving device are capacitively coupledwith each other via the ground (when the reference point path includesthe ground), the reference point path is changed according to positionalrelation between the ground, the transmitting device, the receivingdevice, and the communication medium for example a human body), and thusthere is a fear of the stability of communication being varied.

As described above, in the communication methods that form the twopaths, that is, the communication signal transmitting path and thereference point path as a closed circuit, the use environment greatlyaffects the stability of communication, and it is therefore difficult toperform stable communication.

Further, for example, when such a transmitting device and such areceiving device are applied to mobile devices, and the mobile devicesperform communication via a human body, a manner of for example holdingor wearing the casing of the transmitting device or the receiving devicemay differ depending on the user. That is, it is desirable to enablecommunication in any state as long as the transmitting device and thereceiving device are in proximity to the human body however, in thecommunication methods that form the two paths, that is, thecommunication signal transmitting path and the reference point path as aclosed circuit as described above, it is difficult to secure each of thetwo paths unless positional relation between the communicating devices(the transmitting device and the receiving device) and the communicationmedium is defined.

Conventionally, there is a technique in which the function of each oftwo electrodes included in a communicating device is fixed in order tosecure the two paths. For example, there is a contact type human bodycommunicating device including a wristwatch type ID retaining unit and areading unit for reading the ID retaining unit. In the human bodycommunicating device, wearing positional relation between the twoelectrodes attached to the wristwatch type ID retaining unit and a humanbody is fixed.

However, such a communicating device requires positional relationbetween a user and the device to be in accordance with a specific rule,thus limiting the use environment.

The present invention has been made in view of such a situation, and itis an object of the present invention to impose no limitations onpositional relation between a user and a communicating device, stabilizecommunication, and provide a high degree of convenience by dynamicallycontrolling the functions of electrodes.

Means for Solving the Problems

A communicating device according to the present invention includes:communication processing means for performing communication processing;connecting means for connecting the communication processing means to aplurality of electrodes; and connection controlling means forcontrolling the connecting means to connect a first electrode of theplurality of electrodes, the first electrode being capacitively coupledwith a communication medium, to a first terminal of the communicationprocessing means, and connect a second electrode capacitively coupledwith a space more strongly than the first electrode to a second terminalof the communication processing means.

The connection controlling means can include: signal level detectingmeans for detecting a signal level of a signal for checking a state ofcapacitive coupling of each of the plurality of electrodes withsurroundings when the signal is supplied to each electrode; andcontrolling means for controlling connection of the plurality ofelectrodes to the communication processing means on a basis of thesignal level detected by the signal level detecting means.

The connection controlling means further includes electrode selectingmeans for selecting an electrode to which to supply the signal, and thesignal level detecting means can detect the signal level of the signalwhen the signal is supplied to the electrode selected by the electrodeselecting means.

The connection controlling means further includes retaining means forretaining the signal level detected by the signal level detecting meansfor each electrode, and the controlling means can control the connectionof the plurality of electrodes to the communication processing means onthe basis of the signal level of each electrode, the signal level beingretained by the retaining means.

The connection controlling means can simultaneously supply the signal toall the electrodes, and the signal level detecting means cansimultaneously detect the signal level corresponding to each of all theelectrodes.

The connection controlling means further includes a plurality of loadsconnected to each of the plurality of electrodes and connected in serieswith each other, and the signal level detecting means can detect signallevels occurring at the plurality of loads connected in series with eachother.

The connection controlling means can control the connecting means afterstopping the communication processing by the communication processingmeans.

The connection controlling means can control the connecting means in afree time of the communication processing by the communicationprocessing means.

The connection controlling means can control the connecting means in amanner continuous with the communication processing by the communicationprocessing means.

The connection controlling means can control the connecting meanssimultaneously with a transmission process by the communicationprocessing means, using a transmission signal in the transmissionprocess.

The communication processing means has a transmitting output terminaland a receiving input terminal, and the connection controlling means cancontrol the connecting means to connect the first electrode to thetransmitting output terminal or the receiving input terminal of thecommunication processing means.

A communicating method according to the present invention includes: acommunication controlling step of controlling a communication processingunit for performing communication processing; and a connectioncontrolling step of controlling a connecting unit for connecting thecommunication processing unit for performing the communicationprocessing under control of the communication controlling step to aplurality of electrodes to connect a first electrode of the plurality ofelectrodes, the first electrode being capacitively coupled with acommunication medium, to a first terminal of the communicationprocessing unit, and connect a second electrode capacitively coupledwith a space more strongly than the first electrode to a second terminalof the communication processing unit.

A program according to the present invention includes: a communicationcontrolling step of controlling a communication processing unit forperforming communication processing; and a connection controlling stepof controlling a connecting unit for connecting the communicationprocessing unit for performing the communication processing undercontrol of the communication controlling step to a plurality ofelectrodes to connect a first electrode of the plurality of electrodes,the first electrode being capacitively coupled with a communicationmedium, to a first terminal of the communication processing unit, andconnect a second electrode capacitively coupled with a space morestrongly than the first electrode to a second terminal of thecommunication processing unit.

The communicating device and method and the program according to thepresent invention control a communication processing unit to performcommunication processing, and control a connecting unit for connectingthe communication processing unit to a plurality of electrodes toconnect a first electrode of the plurality of electrodes, the firstelectrode being capacitively coupled with a communication medium, to afirst terminal of the communication processing unit, and connect asecond electrode capacitively coupled with a space more strongly thanthe first electrode to a second terminal of the communication processingunit.

Effect of the Invention

According to the present invention, communication is made possibleirrespective of physical positional relation between a user of acommunicating device and the communicating device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an example of a configuration according toan embodiment of a communication system to which the present inventionis applied.

FIG. 2 is a diagram showing an example of an equivalent circuit of thecommunication system of FIG. 1.

FIG. 3 is a diagram showing an example of a model for a physicalconfiguration of the communication system of FIG. 1.

FIG. 4 is a diagram showing an example of actual use according to anembodiment of the communication system to which the present invention isapplied.

FIG. 5 is a diagram showing another example of use according to anembodiment of the communication system to which the present invention isapplied.

FIG. 6 is a perspective view of an example of external configuration ofa communicating device.

FIG. 7 is a block diagram showing an example of internal configurationof a transmitting device.

FIG. 8 is a block diagram showing an example of detailed configurationof an electrode controlling unit in FIG. 7.

FIG. 9 is a block diagram showing an example of detailed configurationof a transmitting unit in FIG. 7.

FIG. 10 is a flowchart of assistance in explaining a flow of atransmission process.

FIG. 11 is a flowchart of assistance in explaining a flow of anelectrode controlling process.

FIG. 12 is a block diagram showing an example of internal configurationof a receiving device.

FIG. 13 is a block diagram showing an example of detailed configurationof a receiving unit in FIG. 12.

FIG. 14 is a flowchart of assistance in explaining a flow of atransmission and reception process.

FIG. 15 is a block diagram showing an example of internal configurationof a communicating device.

FIG. 16 is a block diagram showing an example of detailed configurationof a communicating unit in FIG. 15.

FIG. 17 is a flowchart of assistance in explaining a flow of acommunication process.

FIGS. 18A, 18, and 18C are diagrams of assistance in explaining examplesof timing of performing the electrode controlling process.

FIG. 19 is a block diagram showing another example of detailedconfiguration of an electrode controlling unit in FIG. 15.

FIG. 20 is a diagram showing an example of configuration of a personalcomputer to which an embodiment of the present invention is applied.

DESCRIPTION OF REFERENCE NUMERALS

1 communication system, 10 transmitting device, 11 transmission signalelectrode, 12 transmission reference electrode, 13 transmitting unit, 20receiving device, 21 received signal electrode, 22 reception referenceelectrode, 23 receiving unit, 30 communication medium, 63-1 signalsource, 63-2 reference point within the transmitting device, 64 Cte, 65Ctg, 66 reference point, 73-1 Rr, 73-2 detector, 73-3 reference pointwithin the receiving device, 74 Cre, 75 Crg, 76 reference point, 117-1Ctb, 117-2 Cth, 117-3 Cti, 127-1 Crb, 127-2 Crh, 127-3 Cri, 131 Rm, 132Cm, 133 Rm, 136 reference point, 180 human body, 200 casing, 211 to 216electrode, 220 hand, 260 transmitting device, 261 electrode controllingunit, 262 electrode unit, 263 transmitting unit, 301 main control unit,302 signal input controlling unit, 303 retaining unit, 304 connectioncontrolling unit, 305 switching controlling unit, 311 signal source, 312switch, 313 detecting unit, 314 connecting unit, 351 transmissioncontrolling unit, 352 transmission signal generating unit, 353amplifying unit, 354 connecting unit, 355 connection controlling unit,370 receiving device, 371 electrode controlling unit, 372 electrodeunit, 373 receiving unit, 401 reception controlling unit, 450communicating device, 451 electrode controlling unit, 452 electrodeunit, 453 communicating unit, 501 communication controlling unit, 613detecting unit, 614 connecting unit

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will hereinafter be described withreference to the drawings. Description will first be made of principlesof communication by a communication system.

FIG. 1 is a diagram showing an example of a configuration according toan embodiment of a communication system to which the present inventionis applied.

The communication system 1 in FIG. 1 includes a transmitting device 10,a receiving device 20, and a communication medium 30. In thecommunication system 1, the transmitting device 10 and the receivingdevice 20 transmit and receive a signal via the communication medium 30.That is, in the communication system 1, a signal transmitted by thetransmitting device 10 is transmitted via the communication medium 30,and then received by the receiving device 20.

The transmitting device 10 has a transmission signal electrode 11, atransmission reference electrode 12, and a transmitting unit 13. Thetransmission signal electrode 11 is one electrode of the electrode pairprovided to transmit a signal to be transmitted via the communicationmedium 30. The transmission signal electrode 11 is provided in such amanner as to be capacitively coupled to the communication medium 30 morestrongly than the transmission reference electrode 12 as anotherelectrode of the electrode pair. The transmitting unit 13 is providedbetween the transmission signal electrode 11 and the transmissionreference electrode 12, The transmitting unit 13 gives an electricsignal (potential difference) desired to be transmitted to the receivingdevice 20 between these electrodes.

The receiving device 20 has a received signal electrode 21, a receptionreference electrode 22, and a receiving unit 23. The received signalelectrode 21 is one electrode of the electrode pair provided to receivethe signal transmitted via the communication medium 30. The receivedsignal electrode 21 is provided in such a manner as to be capacitivelycoupled to the communication medium 30 more strongly than the receptionreference electrode 22 as another electrode of the electrode pair. Thereceiving unit 23 is provided between the received signal electrode 21and the reception reference electrode 22. The receiving unit 23 detectsan electric signal (potential difference) generated between theseelectrodes by the signal transmitted via the communication medium 30,converts the electric signal into a desired electric signal, and therebyreconstructs the electric signal generated by the transmitting unit 13in the transmitting device 10.

The communication medium 30 is formed by a material having a physicalcharacteristic that allows the electric signal to be transmitted, forexample, an electric conductor, a dielectric or the like. For example,the communication medium 30 is formed by a conductor typified by a metalsuch as copper, iron, aluminum or the like, a dielectric typified bypure water, rubber, glass or the like, or a material having bothproperties of a conductor and properties of a dielectric, such forexample as a living body or the like as a complex of the conductor andthe dielectric or an electrolytic solution such as a saline solution orthe like, In addition, the communication medium 30 may have any shape.For example, the communication medium 30 may be of the shape of a line,of the shape of a plate, of the shape of a sphere, a prism, a circularcylinder or the like, or may further be of any arbitrary shape otherthan these shapes.

Description will first be made of relation between each electrode andthe communication medium or a space surrounding the devices in such acommunication system 1. Incidentally, suppose in the following that thecommunication medium 30 is a perfect conductor for convenience ofdescription. In addition, suppose that there is a space between thetransmission signal electrode 11 and the communication medium 30 andthere is a space between the received signal electrode 21 and thecommunication medium 30, and that there is no electric coupling betweenthe transmission signal electrode 11 and the communication medium 30 andthere is no electric coupling between the received signal electrode 21and the communication medium 30. That is, a capacitance is formedbetween the transmission signal electrode 11 or the received signalelectrode 21 and the communication medium 30.

The transmission reference electrode 12 is disposed so as to face aspace around the transmitting device 10. The reception referenceelectrode 22 is disposed so as to face a space around the receivingdevice 20. Generally, when a conductor sphere is present in a space, acapacitance is formed between the conductor sphere and the space. Forexample, when the shape of the conductor is a sphere with a radius r[m], the capacitance C is obtained by the following Equation (1).

[Equation 1]

C=4π∈r [F]  (1)

In Equation (1), π denotes a ratio of the circumference of a circle toits diameter, and ∈ denotes a dielectric constant, which is obtained bythe following Equation (2).

[Equation 2]

∈=∈_(r)×∈₀  (2)

In Equation (2), ∈₀ to denotes a dielectric constant in a vacuum and is8.854×10⁻¹² [F/m], and ∈_(r) denotes a relative dielectric constant,which represents a ratio to the dielectric constant ∈₀ in the vacuum.

As shown in the above Equation (1), the larger the radius r, the largerthe capacitance C. Incidentally, the magnitude of the capacitance C of aconductor having a complex shape other than a sphere cannot be expressedsimply as in the above Equation (1). It is obvious, however, that themagnitude of the capacitance C of the conductor changes according to themagnitude of the surface area of the conductor.

As described above, the transmission reference electrode 12 forms acapacitance with the space surrounding the transmitting device 10, andthe reception reference electrode 22 forms a capacitance with the spacesurrounding the receiving device 20. That is, it is shown that as viewedfrom a virtual point at infinity outside the transmitting device 10 andthe receiving device 20, the potentials of the transmission referenceelectrode 12 and the reception reference electrode 22 increaseresistance thereof to variation as the capacitances are increased.

Incidentally, though for convenience of description or in a context orthe like, a capacitor may herein be expressed simply as a capacitance,the capacitor and the capacitance have the same meaning. In addition,suppose that the transmitting device 10 and the receiving device in FIG.1 are arranged such that a sufficient distance is maintained between thedevices, and that therefore effects of the transmitting device 10 andthe receiving device 20 on each other can be ignored. Further, supposethat the transmission signal electrode 11 in the transmitting device 10is capacitively coupled with only the communication medium 30, and thatthe transmission reference electrode 12 is located at a sufficientdistance from the transmission signal electrode 11, so that effects ofthe transmission reference electrode 12 and the transmission signalelectrode 11 on each other can be ignored (the transmission referenceelectrode 12 and the transmission signal electrode 11 are notcapacitively coupled with each other). Similarly, suppose that thereceived signal electrode 21 in the receiving device 20 is capacitivelycoupled with only the communication medium 30, and that the receptionreference electrode 22 is located at a sufficient distance from thereceived signal electrode 21, so that effects of the reception referenceelectrode 22 and the received signal electrode 21 on each other can beignored (the reception reference electrode 22 and the received signalelectrode 21 are not capacitively coupled with each other). Further, inpractice, the transmission signal electrode 11, the received signalelectrode 21, and the communication medium 30 are disposed within aspace, and therefore the transmission signal electrode 11, the receivedsignal electrode 21, and the communication medium 30 each have acapacitance in relation to the space. For convenience of description,however, suppose that these capacitances can be ignored.

FIG. 2 is a diagram in which the communication system 1 of FIG. 1 isrepresented by an equivalent circuit. That is, a communication system 50shown in FIG. 2 is equivalent in effect to the communication system 1.

Specifically, the communication system 50 has a transmitting device 60,a receiving device 70, and a connection line 80. The transmitting device60 corresponds to the transmitting device 10 in the communication system1 shown in FIG. 1. The receiving device 70 corresponds to the receivingdevice 20 in the communication system 1 shown in FIG. 1. The connectionline 80 corresponds to the communication medium 30 in the communicationsystem 1 shown in FIG. 1.

In the transmitting device 60 in FIG. 2, a signal source 63-1 and areference point 63-2 within the transmitting device correspond to thetransmitting unit 13 in FIG. 1. The signal source 63-1 generates, as asignal for transmission, a sine wave having a specific period ω×t (rad),where t [s] denotes time, and ω [rad/s] denotes an angular frequency,which can be expressed by the following Equation (3).

[Equation 3]

ω=2πf [rad/s]  (3)

In Equation (3), a denotes a ratio of the circumference of a circle toits diameter, and f [Hz] denotes the frequency of the signal generatedby the signal source 63-1. The reference point 63-2 within thetransmitting device is a point connected to a ground of a circuit withinthe transmitting device 60. That is, one of terminals of the signalsource 63-1 is set to a predetermined reference potential of the circuitwithin the transmitting device 60.

Cte 64 is a capacitor, and represents a capacitance between thetransmission signal electrode 11 and the communication medium 30 inFIG. 1. That is, Cte 64 is provided between the connection line 80 andthe terminal of the signal source 63-1 which terminal is on an oppositeside from the reference point 63-2 within the transmitting device. Ctg65 is a capacitor, and represents a capacitance of the transmissionreference electrode 12 in FIG. 1 in relation to the space. Ctg 65 isdisposed between the terminal of the signal source 63-1 which terminalis on the side of the reference point 63-2 within the transmittingdevice and a reference point 66 representing a point at infinity(virtual point) on the space with the transmitting device 60 as areference.

In the receiving device 70 in FIG. 2, Rr 73-1, a detector 73-2, and areference point 73-3 within the receiving device correspond to thereceiving unit 23 in FIG. 1. Rr 73-1 is a load resistance (receptionload) for extracting a received signal. The detector 73-2 formed by anamplifier detects a potential difference across Rr 73-1, and amplifiesthe potential difference. The reference point 73-3 within the receivingdevice is a point connected to a ground of a circuit within thereceiving device 70. That is, one of terminals of Rr 73-1 (one of inputterminals of the detector 73-2) is set to a predetermined referencepotential of the circuit within the receiving device 70.

Incidentally, the detector 73-2 may have other functions of for exampledemodulating a detected modulated signal and decoding encodedinformation included in the detected signal.

Cre 74 is a capacitor, and represents a capacitance between the receivedsignal electrode 21 and the communication medium 30 in FIG. 1. That is,Cre 74 is provided between the connection line 80 and the terminal of Pr73-1 which terminal is on an opposite side from the reference point 73-3within the receiving device. Crg 75 is a capacitor, and represents acapacitance of the reception reference electrode 22 in FIG. 1 inrelation to the space. Crg 75 is disposed between the terminal of Rr73-1 which terminal is on the side of the reference point 73-3 withinthe receiving device and a reference point 76 representing a point atinfinity (virtual point) on the space with the receiving device 20 as areference.

The connection line 80 represents the communication medium 30 as aperfect conductor. Incidentally, in the communication system 50 in FIG.2, Ctg 65 and Crg 75 are expressed as electrically connected to eachother via the reference point 66 and the reference point 76 on theequivalent circuit. In practice, however, these capacitors do not needto be electrically connected to each other, and it suffices for each ofthe capacitors to form a capacitance in relation to the spacesurrounding the transmitting device 60 or the receiving device 70. It isimportant to know that when there is a conductor, a capacitanceproportional to the magnitude of the surface area of the conductor isalways formed between the conductor and a surrounding space.Incidentally, the reference point 66 and the reference point 76 do notneed to be electrically connected to each other, and may have potentialsindependent of each other.

When the communication medium 30 in FIG. 1 is a perfect conductor, forexample, the conductivity of the connection line 80 is infinite.Therefore the length of the connection line 80 in FIG. 2 does not affectcommunication, incidentally, when the communication medium 30 is aconductor having a sufficient conductivity, a distance between thetransmitting device and the receiving device does not affect thestability of communication practically. Thus, in such a case, thedistance between the transmitting device 60 and the receiving device 70may be any length.

In the communication system 50, a circuit formed of the signal source63-1, Rr 73-1, Cte 64, Ctg 65, Cre 74, and Crg 75 is formed. A combinedcapacitance C, of the four capacitors (Cte 64, Ctg 65, the Cre capacitor74, and Crg 75) connected in series with each other can be expressed bythe following Equation (4).

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack & \; \\{C_{x} = {\frac{1}{\frac{1}{Cte} + \frac{1}{Ctg} + \frac{1}{Cre} + \frac{1}{Crg}}\mspace{14mu}\lbrack F\rbrack}} & (4)\end{matrix}$

A sine wave v_(t)(t) generated by the signal source 63-1 is expressed bythe following Equation (5).

[Equation 5]

V _(t)(t)=V _(m)×sin(ωt+θ) [V]  (5)

Where V_(m) [V] denotes a maximum amplitude voltage of a signal sourcevoltage, and θ [rad] denotes an initial phase angle. An effective valueV_(trms) [V] of the voltage generated by the signal source 63-1 can beobtained by the following Equation (6).

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 6} \right\rbrack & \; \\{V_{trms} = {\frac{V_{m}}{\sqrt{2}}\mspace{14mu}\lbrack V\rbrack}} & (6)\end{matrix}$

A combined impedance Z of the whole circuit can be obtained by thefollowing Equation (7).

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 7} \right\rbrack & \; \\\begin{matrix}{Z = \sqrt{{Rr}^{2} + \frac{1}{\left( {\omega \; C_{x}} \right)^{2}}}} \\{= {\sqrt{{Rr}^{2} + \frac{1}{\left( {2\pi \; {fC}_{x}} \right)^{2}}}\mspace{14mu}\lbrack\Omega\rbrack}}\end{matrix} & (7)\end{matrix}$

Thus, an effective value v_(rims) [V] of a voltage across Rr 73-1 can beobtained by the following Equation (8).

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 8} \right\rbrack & \; \\\begin{matrix}{V_{rrms} = {\frac{Rr}{Z} \times V_{rrms}}} \\{= {\frac{Rr}{\sqrt{{Rr}^{2} + \frac{1}{\left( {2\pi \; {fC}_{x}} \right)^{2}}}} \times {V_{rrms}\mspace{14mu}\lbrack V\rbrack}}}\end{matrix} & (8)\end{matrix}$

Hence, as shown in Equation (8), as the resistance value of Rr 73-1 isincreased, and as the term 1/(2×πf×C_(x))²) is reduced with increase inthe capacitance C_(x) and increase in frequency f [Hz] of the signalsource 63-1, a signal having a greater magnitude can be generated acrossRr 73-1.

For example, results of calculation of the effective value V_(rrms) [V]of the voltage across Rr 73-1 when the effective value V_(trms) [V] ofthe voltage generated by the signal source 63-1 in the transmittingdevice 60 is fixed at 2 [V], the frequency f of the signal generated bythe signal source 63-1 is set at 1 [MHz], 10 [MHz], or 100 [MHz], theresistance value of Rr 73-1 is set at 10 [KΩ], 100 [KΩ], or 1 [MΩ], andthe capacitance C_(x) of the whole circuit is set at 0.1 [pF], 1 [pF],or 10 [pF] show that other conditions being equal, the effective valueV_(rrms) is higher when the frequency f is 10 [MHz] than when thefrequency f is 1 [MHz], is higher when the resistance value of Rr 73-1as reception load is 1 [MΩ] than when the resistance value of Rr 73-1 is10 [KΩ], and is higher when the capacitance C_(x) is 10 [pF] than whenthe capacitance C_(x) is 0.1 [pF]. That is, as the value of thefrequency f, the resistance value of Rr 73-1, and the capacitance C_(x)are increased, the effective value V_(rrms) of higher voltage isobtained.

Incidentally, when a transmitted signal has a very low signal level,communication is made possible by for example amplifying the signaldetected by the detector 73-2 in the receiving device 60.

Description will next be made of a case where the present communicationsystem is physically formed in practice. FIG. 3 is a diagram showing anexample of a model for computing parameters occurring on the system whenthe above-described communication system is physically formed inpractice.

That is, a communication system 100 has a transmitting device 110, areceiving device 120, and a communication medium 130. The communicationsystem 100 corresponds to the above-described communication system 1(communication system 50). Only parameters to be evaluated aredifferent, and the communication system 100 has basically the sameconfiguration as the communication system 1 and the communication system50.

That is, making description by comparison with the communication system1 of FIG. 1, the transmitting device 110 corresponds to the transmittingdevice 10, the receiving device 120 corresponds to the receiving device20, and the communication medium 130 corresponds to the communicationmedium 30.

The transmitting device 110 has a transmission signal electrode 111corresponding to the transmission signal electrode 11, a transmissionreference electrode 112 corresponding to the transmission referenceelectrode 12, and a signal source 113 corresponding to the transmittingunit 13. That is, the transmission signal electrode 111 is connected toone of terminals on both sides of the signal source 113, and thetransmission reference electrode 112 is connected to the other terminal.The transmission signal electrode 111 is disposed in proximity to thecommunication medium 130. The transmission reference electrode 112 isformed in such a manner as to have a capacitance in relation to a spaceexternal to the transmitting device 110. Incidentally, while the signalsource 63-1 and the reference point 63-2 within the transmitting devicein FIG. 2 correspond to the transmitting unit 13, the reference pointwithin the transmitting device is omitted in FIG. 3 for convenience ofdescription.

As with the transmitting device 110, the receiving device 120 has areceived signal electrode 121 corresponding to the received signalelectrode 21, a reception reference electrode 122 corresponding to thereception reference electrode 22, and Rr 123-1 and a detector 123-2corresponding to the receiving unit 23. That is, the received signalelectrode 121 is connected to one of terminals on both sides of Rr123-1, and the reception reference electrode 122 is connected to theother terminal. The received signal electrode 121 is disposed inproximity to the communication medium 130. The reception referenceelectrode 122 is formed in such a manner as to have a capacitance inrelation to a space external to the receiving device 120. Incidentally,while Rr 73-1, the detector 73-2, and the reference point 73-3 withinthe receiving device in FIG. 2 correspond to the receiving unit 23, thereference point within the receiving device is omitted in FIG. 3 forconvenience of description.

Incidentally, suppose that the communication medium 130 is a perfectconductor as in the cases of FIG. 1 and FIG. 2. Suppose that thetransmitting device 110 and the receiving device 120 are arranged at asufficient distance from each other, and that effects of thetransmitting device 110 and the receiving device 120 on each other canbe ignored.

Description will be made of the parameters. A capacitance Cte 114between the transmission signal electrode 111 and the communicationmedium 130 corresponds to Cte 64 in FIG. 2. A capacitance of thetransmission reference electrode 112 in relation to the space (acapacitance between the transmission reference electrode 112 and areference point 116-1 representing a virtual point at infinity from thetransmission reference electrode 112 on the space) Ctg 115 correspondsto Ctg 65 in FIG. 2. The reference point 116-1 and a reference point116-2 representing a virtual point at infinity from the transmittingdevice 110 on the space correspond to the reference point 66 in FIG. 2.The transmission signal electrode 111 is a disk-shaped electrode havingan area Ste [m²], and is located at a minute distance dte [m] from thecommunication medium 130. The transmission reference electrode 112 isalso a disk-shaped electrode, and has a radius rtg [m].

On the receiving device 120 side, a capacitance Cre 124 between thereceived signal electrode 121 and the communication medium 130corresponds to Cre 74 in FIG. 2. A capacitance of the receptionreference electrode 122 in relation to the space (a capacitance betweenthe reception reference electrode 122 and a reference point 126-1representing a virtual point at infinity from the reception referenceelectrode 122 on the space) Crg 125 corresponds to Crg 75 in FIG. 2. Thereference point 126-1 and a reference point 126-2 representing a virtualpoint at infinity from the receiving device 120 on the space correspondto the reference point 76 in FIG. 2. The received signal electrode 121is a disk-shaped electrode having an area Sre [m²], and is located at aminute distance dre [m] from the communication medium 130. The receptionreference electrode 122 is also a disk-shaped electrode, and has aradius rrg [m].

Further, new parameters are added to the communication system 100 ofFIG. 3 as follows.

For example, added to the transmitting device 110 as new parameters area capacitance Ctb 117-1 formed between the transmission signal electrode111 and the transmission reference electrode 112, a capacitance Cth117-2 formed between the transmission signal electrode 111 and the space(a capacitance between the transmission signal electrode 111 and areference point 116-2 representing a virtual point at infinity from thetransmission signal electrode 111 on the space), and a capacitance Cti117-3 formed between the transmission reference electrode 112 and thecommunication medium 130.

Added to the receiving device 120 as new parameters are a capacitanceCrb 127-1 formed between the received signal electrode 121 and thereception reference electrode 122, a capacitance Crh 127-2 formedbetween the received signal electrode 121 and the space (a capacitancebetween the received signal electrode 121 and a reference point 126-2representing a virtual point at infinity from the received signalelectrode 121 on the space), and a capacitance Cri 127-3 formed betweenthe reception reference electrode 122 and the communication medium 130.

Further, a capacitance Cm 132 formed between the communication medium130 and the space (a capacitance between the communication medium 130and a reference point 136 representing a virtual point at infinity fromthe communication medium 130 on the space) is added to the communicationmedium 130 as a new parameter. In addition, since the communicationmedium 130 in practice has an electric resistance depending on the size,material and the like of the communication medium 130, resistance valuesRm 131 and Rm 133 as resistance components of the communication medium130 are added as new parameters.

Incidentally, though omitted in the communication system 100 of FIG. 3,when the communication medium has not only conductivity but alsodielectric properties, a capacitance according to the dielectricproperties is also formed. When the communication medium does not haveconductivity but has dielectric properties, coupling between thetransmission signal electrode 111 and the received signal electrode 121is provided by a capacitance determined by the dielectric constant,distance, size, and disposition of the dielectric.

In this case, it is assumed that the transmitting device 110 and thereceiving device 120 are separated from each other at a distance suchthat an element of capacitive coupling can be ignored (effects ofcapacitive coupling between the transmitting device 110 and thereceiving device 120 can be ignored). If the distance is short,depending on positional relation between each electrode within thetransmitting device 110 and each electrode within the receiving device120, capacitances between the electrodes may need to be consideredaccording to the above-described way of thinking.

The communication system 100 having such parameters has characteristicsas follows.

For example, the higher the value of Cte 114 (the higher thecapacitance), the greater the magnitude of the signal applied by thetransmitting device 110 to the communication medium 130. In addition,the higher the value of Ctg 115 (the higher the capacitance), thegreater the magnitude of the signal applied by the transmitting device110 to the communication medium 130. Further, the lower the value of Ctb117-1 (the lower the capacitance), the greater the magnitude of thesignal applied by the transmitting device 110 to the communicationmedium 130. In addition, the lower the value of Cth 117-2 (the lower thecapacitance), the greater the magnitude of the signal applied by thetransmitting device 110 to the communication medium 130. Further, thelower the value of Cti 117-3 (the lower the capacitance), the greaterthe magnitude of the signal applied by the transmitting device 110 tothe communication medium 130.

The higher the value of Cre 124 (the higher the capacitance), thegreater the magnitude of the signal extracted from the communicationmedium 130 by the receiving device 120. In addition, the higher thevalue of Crg 125 (the higher the capacitance), the greater the magnitudeof the signal extracted from the communication medium 130 by thereceiving device 120. Further, the lower the value of Crb 127-1 (thelower the capacitance), the greater the magnitude of the signalextracted from the communication medium 130 by the receiving device 120.In addition, the lower the value of Crh 127-2 (the lower thecapacitance), the greater the magnitude of the signal extracted from thecommunication medium 130 by the receiving device 120. Further, the lowerthe value of Cri 127-3 (the lower the capacitance), the greater themagnitude of the signal extracted from the communication medium 130 bythe receiving device 120. In addition, the lower the value of Rr 123-1(the higher the resistance), the greater the magnitude of the signalextracted from the communication medium 130 by the receiving device 120.

The lower the values of Rm 131 and Rm 133 as resistance components ofthe communication medium 130 (the lower the resistances), the greaterthe magnitude of the signal applied by the transmitting device 110 tothe communication medium 130. In addition, the lower the value of Cm 132as the capacitance of the communication medium 130 in relation to thespace (the lower the capacitance), the greater the magnitude of thesignal applied by the transmitting device 110 to the communicationmedium 130.

The magnitude of capacitance of a capacitor is substantiallyproportional to the magnitude of the surface area of the electrode.Therefore it is generally desirable to increase the size of eachelectrode as much as possible. However, simply increasing the size ofelectrodes may also increase capacitances between the electrodes. Inaddition, an extreme ratio between the sizes of electrodes may decreaseefficiency. It is thus necessary to determine the size, arrangementposition and the like of each electrode in consideration of a totalbalance.

Incidentally, with the characteristics of the above-describedcommunication system 100, efficient communication is made possible byviewing the present equivalent circuit from a viewpoint of impedancematching and determining each parameter in a frequency band of highfrequencies of the signal source 113. By raising the frequency, it ispossible to secure a reactance even with a low capacitance, so that eachdevice can be miniaturized easily.

The reactance of a capacitor is generally increased with decrease infrequency. On the other hand, the communication system 100 operatesbased on capacitance coupling, and therefore this determines a lowerlimit of the frequency of the signal generated by the signal source 113.In addition, an arrangement of Rm 131, Cm 132, and Rm 133 forms alow-pass filter, and therefore characteristics thereof determine anupper limit of the frequency.

A specific numerical value of each parameter will next be considered.Incidentally, suppose in the following that the communication system 100is placed in the air for convenience of description. In addition,suppose that the transmission signal electrode 111, the transmissionreference electrode 112, the received signal electrode 121, and thereception reference electrode 122 of the communication system 100 areeach a conductor disk having a diameter of 5 cm.

Supposing that the interval dte between the transmission signalelectrode 111 and the communication medium 130 is 5 mm, the value of thecapacitance Cte 114 formed by the transmission signal electrode 111 andthe communication medium 130 is obtained by the following Equation (9).

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 9} \right\rbrack & \; \\\begin{matrix}{{Cte} = {ɛ \times \frac{Ste}{dte}}} \\{= \frac{\left( {8.854 \times 10^{- 12}} \right) \times \left( {2 \times 10^{- 3}} \right)}{5 \times 10^{- 3}}} \\{\approx {3.5\mspace{14mu}\lbrack{pF}\rbrack}}\end{matrix} & (9)\end{matrix}$

Assume that Equation (9) can be adapted to Ctb 117-1 as the capacitancebetween the electrodes. While the equation essentially holds when thearea of the electrodes is sufficiently large as compared with theinterval as described above, an approximation may be made by thisequation in this case. Supposing that the interval between theelectrodes is 5 cm, Ctb 117-1 is expressed by the following Equation(10).

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 10} \right\rbrack & \; \\\begin{matrix}{{Ctb} = {ɛ \times \frac{Ste}{d}}} \\{= \frac{\left( {8.854 \times 10^{- 12}} \right) \times \left( {2 \times 10^{- 3}} \right)}{5 \times 10^{- 2}}} \\{\approx {0.35\mspace{14mu}\lbrack{pF}\rbrack}}\end{matrix} & (10)\end{matrix}$

An assumption is made in this case that when the interval between thetransmission signal electrode 111 and the communication medium 130 isshort, the transmission signal electrode 111 is weakly coupled with thespace. Therefore suppose that the value of Cth 117-2 is sufficientlylower than the value of Cte 114, and that the value of Cth 117-2 can beset to one tenth of the value of Cte 114 as expressed by Equation (11).

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 11} \right\rbrack & \; \\{{Cth} = {\frac{Cte}{10} = {0.35\mspace{14mu}\lbrack{pF}\rbrack}}} & (11)\end{matrix}$

Ctg 115 indicating the capacitance formed by the transmission referenceelectrode 112 and the space can be obtained by the following Equation(12).

[Equation 12]

Ctg=8×8.854×10⁻¹²×2.5×10⁻²≈1.8 [pF]  (12)

Since the transmission signal electrode 111 and the communication medium130 are situated at substantially the same position, the value of Cti117-3 is considered to be equal to Ctb 117-1 as follows.

Cti=Ctb=0.35 [pF]

When the formation (size, placement position and the like) of eachelectrode in the receiving device 120 is the same as in the transmittingdevice 110, the parameters of the receiving device 120 are set in thesame manner as the parameters of the transmitting device 110 as follows.

Cre=Cte=3.5 [pF]

Crb=Ctb=0.35 [pF]

Crh=Cth=0.35 [pF]

Crg=Ctg=1.8 [pF]

Cri=Cti=0.35 [pF]

For convenience of description, suppose in the following that thecommunication medium 130 is an object having characteristics close tothose of a living body of about a size of a human body. Suppose that anelectric resistance of the communication medium 130 from the position ofthe transmission signal electrode 111 to the position of the receivedsignal electrode 121 is 1 [MΩ], and that the values of Rm 131 and Rm 133are each 500 [KΩ]. Suppose that the value of the capacitance Cm 132formed between the communication medium 130 and the space is 100 [pF].Further, suppose that the signal source 113 generates a sine wave havinga maximum value of 1 [V] and a frequency of 10 [MHz].

When a simulation is performed using the above parameters, a differencebetween a maximum value and a minimum value (a difference between peakvalues) of the waveform of a received signal is observed to be about 10[μV]. Thus, by amplifying this by an amplifier (detector 123-2) having asufficient gain, it is possible to reconstruct the signal of thetransmitting side (signal generated in the signal source 113) on thereceiving side.

Thus, the above-described communication system to which the presentinvention is applied eliminates a need for a physical reference pointpath, and can achieve communication by only a communication signaltransmitting path. Therefore a communication environment not limited bya use environment can be readily provided.

A concrete example of application of a communication system as describedabove will next be described. For example, a communication system asdescribed above can use a living body as a communication medium. FIG. 4is a schematic diagram showing an example of a communication system whencommunication is performed via a human body. The communication system150 in FIG. 4 is a system in which music data is transmitted from atransmitting device 160 attached to an arm part of a human body, and areceiving device 170 attached to a head part of the human body receivesthe music data, converts the music data into audio, and outputs theaudio to allow the user to listen to the audio. The communication system150 corresponds to the above-described communication systems (forexample the communication system 1). The transmitting device 160 and thereceiving device 170 correspond to the transmitting device 10 and thereceiving device 20, respectively. The human body 180 in thecommunication system 150 is a communication medium, and corresponds tothe communication medium 30 in FIG. 1.

Specifically, the transmitting device 160 has a transmission signalelectrode 161, a transmission reference electrode 162, and atransmitting unit 163. The transmission signal electrode 161, thetransmission reference electrode 162, and the transmitting unit 163correspond to the transmission signal electrode 11, the transmissionreference electrode 12, and the transmitting unit 13, respectively, inFIG. 1. The receiving device 170 has a received signal electrode 171, areception reference electrode 172, and a receiving unit 173. Thereceived signal electrode 171, the reception reference electrode 172,and the receiving unit 173 correspond to the received signal electrode21, the reception reference electrode 22, and the receiving unit 23,respectively, in FIG. 1.

Thus, the transmitting device 160 and the receiving device 170 areplaced such that the transmission signal electrode 161 and the receivedsignal electrode 171 are in contact with or in proximity to the humanbody 180 as a communication medium. Since it suffices for thetransmission reference electrode 162 and the reception referenceelectrode 172 to be in contact with a space, coupling with a ground inthe vicinity or coupling between the transmitting device and thereceiving device (or electrodes) is not required.

FIG. 5 is a diagram of assistance in explaining another example ofrealizing the communication system 150. In FIG. 5, the receiving device170 is in contact with (or in proximity to) a sole part of the humanbody 180, and communicates with the transmitting device 160 attached toan arm part of the human body 180. Also in this case, the transmissionsignal electrode 161 and the received signal electrode 171 are disposedso as to be in contact with (or in proximity to) the human body 180 as acommunication medium, and the transmission reference electrode 162 andthe reception reference electrode 172 are disposed so as to face thespace. This application example cannot be realized by the conventionaltechniques using a ground as one communication path, in particular.

That is, the communication system 150 as described above eliminates theneed for a physical reference point path, and can achieve communicationby only a communication signal transmitting path. Therefore acommunication environment not limited by a use environment can bereadily provided.

In the communication system as described above, a method of modulationof a signal to be passed through the communication medium is notparticularly limited as long as both the transmitting device and thereceiving device can deal with the modulation method. An optimum methodcan be selected in consideration of characteristics of the communicationsystem as a whole. Specifically, the modulation method may provide oneof a baseband, an amplitude-modulated, and a frequency-modulated analogsignal and a baseband, an amplitude-modulated, a frequency-modulated,and a phase-modulated digital signal, or a mixture of a plurality ofsignals.

Further, in the communication system as described above, a plurality ofcommunications may be established using one communication medium, sothat full-duplex communication, communication between a plurality ofdevices by a single communication medium, or the like can be performed.

Methods for realizing such multiplex communication include for example aspread spectrum system, a frequency band division system, a timedivision system and the like. By communicating using each such system,the communication system can perform simultaneous communication with aplurality of devices using the same communication medium, such forexample as communication between a plurality of devices and a singledevice, communication between a plurality of devices and a plurality ofdevices, and the like. Further, two or more of the above-describedmethods may be combined with each other, of course.

It is particularly important in a specific application that thetransmitting device and the receiving device can simultaneouslycommunicate with a plurality of other devices. Assuming application to aticket for a transportation, for example, when a user carrying both adevice A having information on a commuter pass and a device B having anelectronic money function uses an automatic ticket gate, a system asdescribed above is used, and thereby simultaneous communication with thedevice A and the device B is performed. When a used section includes asection not covered by the commuter pass, the system can be usedconveniently to deduct an amount of money that is lacking from theelectronic money of the device B.

As described above, the transmitting device 10 and the receiving device20 do not need to construct a closed circuit using a referenceelectrode, and can easily perform a stable communication processunaffected by an environment only by transmitting and receiving a signalvia signal electrodes. Incidentally, since a structure for thecommunication process is simplified, the communication system 1 caneasily use various communication systems such as modulation, encoding,encryption, multiplexing and the like in combination with each other.

When such a communication system is used to perform communication viathe human body 180 as shown in FIG. 4, for example, it is preferablethat the transmitting device and the receiving device be miniaturized asmobile devices. While a method of use is conceivable in which thetransmitting device and the receiving device are for example fixed to anarm, a leg or the like using a belt or the like so that positionalrelation between the devices and the human body is stabilized, a methodof use in which a user freely holds or places the transmitting deviceand the receiving device as in a case of a portable type telephone, forexample, is also assumed. Therefore a higher degree of freedom of awearing method (positional relation between the devices and the humanbody) is desirable, and widens a range of applications.

For example, as shown in FIG. 6, a casing of the transmitting device 10in FIG. 1 is formed as a casing 200. Electrodes 211 to 216 to be used asthe transmission signal electrode 11 and the transmission referenceelectrode 12 are provided in external surfaces of the casing 200. When auser holds such a transmitting device by a hand 220, the transmittingdevice 10 can perform communication via the human body as shown in FIG.4 or FIG. 5.

Incidentally, each of the electrodes 211 to 216 can be used as thetransmission signal electrode 11 or the transmission reference electrode12. That is, by controlling (changing) connections of the electrodes 211to 216 to an internal circuit, the transmitting device 10 can usearbitrary electrodes as the transmission signal electrode 11, and useother arbitrary electrodes as the transmission reference electrode 12.

In such a case, however, it is not possible to predict how the user (thehand 220 of the user) holds the casing 200. Therefore, when theelectrodes 211 to 216 are fixedly assigned the role of one of thetransmission signal electrode 11 and the transmission referenceelectrode 12, both the transmission signal electrode 11 and thetransmission reference electrode 12 may be close to the hand 220 as acommunication medium in similar manners to each other depending on aholding state. In this case, a desirable communication environment maynot be obtained.

Accordingly, the communication device 10 in FIG. 6 controls theconnection of the electrodes 211 to 216 to the internal circuitaccording to the position of the hand 220 to thereby optimize thepositional relation between the transmission signal electrode(electrodes used as the transmission signal electrode) and thetransmission reference electrode (electrodes used as the transmissionreference electrode) and the communication medium (hand 220). Forexample, in FIG. 6, the transmitting device 10 connects the electrode212, the electrode 213, the electrode 215, and the electrode 216 coveredby the hand 220 to the internal circuit so that the electrode 212, theelectrode 213, the electrode 215, and the electrode 216 are used as thetransmission signal electrode 11, and connects the other electrodes 211and 214 to the internal circuit so that the electrodes 211 and 214 areused as the transmission reference electrode 12. In other words, thecommunication device 10 performs control so as to optimize thepositional relation between the communication medium and the electrodepair (electrode pair formed by the transmission signal electrode 11 andthe transmission reference electrode 12).

Incidentally, the transmitting device 10 can control the connection soas to use a plurality of electrodes as the transmission signal electrode11 or the transmission reference electrode 12. In addition, thetransmitting device 10 does not need to make connection so as to use allthe electrodes as the transmission signal electrode 11 or the receptionreference electrode 12, and there may be unconnected electrodes. In thecase of FIG. 6, for example, electrodes only partly covered by the hand220, such as the electrode 212, the electrode 213, and the electrode215, may be disconnected. By thus controlling the connection, thetransmitting device 10 is for example able to use only electrodes thatcan be clearly distinguished as electrodes capacitively coupled with thecommunication medium strongly or weakly among a group of electrodes asthe transmission signal electrode 11 or the transmission referenceelectrode 12, and not to use electrodes capacitively coupled with thecommunication medium to a medium degree (electrodes that cannot beclearly distinguished as electrodes to be used as the transmissionsignal electrode 11 or to be used as the transmission referenceelectrode 12). The transmitting device 10 can thereby set thetransmission signal electrode 11 and the transmission referenceelectrode having an optimum positional relation to the communicationmedium.

FIG. 7 is a block diagram showing an example of configuration of anembodiment of the transmitting device in this case.

The transmitting device 260 in FIG. 7 has an electrode controlling unit261, an electrode unit 262, and a transmitting unit 263. The electrodeunit 262 has an electrode 271 and an electrode 272 as a pair ofelectrodes having the shape of a disk, for example, and capacitivelycoupled with an outside. The electrode controlling unit 261 controlsconnection of each electrode of the electrode unit 262 to thetransmitting unit 263. The transmitting unit 263 performs a process oftransmitting a signal via the electrode unit 262.

The transmitting device 260 corresponds to the transmitting device 10 inFIG. 1. The transmitting device 260 outputs a signal to a communicationmedium 280 corresponding to the communication medium 30, usingelectrostatic induction, and thereby transmits the signal to a receivingdevice via the communication medium 280, which is a conductor or adielectric. The electrode pair of the electrode 271 and the electrode272 of the electrode unit 262 corresponds to the electrode pair of thetransmission signal electrode 11 and the transmission referenceelectrode 12 in FIG. 1. The transmitting unit 263 corresponds to thetransmitting unit 13 in FIG. 1.

That is, one of the electrode 271 and the electrode 272 is connected asthe transmission signal electrode 11 to the transmitting unit 263, andthe other is connected as the transmission reference electrode 12 to thetransmitting unit 263. The electrode controlling unit 262 checks a stateof capacitive coupling (magnitude of capacitance) of the electrode 271and the electrode 272 with the external part, and controls theconnection of the electrode 271 and the electrode 272 to thetransmitting unit 263 to be optimized according to the state.

For example, suppose that as shown in FIG. 7, the communication medium280 serving as a communication path and having conductivity ordielectric properties approaches the electrode 271. At this time, theelectrode 272 is facing a free space, and forms a capacitance Ctg 295with the free space. On the other hand, as the communication medium 280approaches the electrode 271, capacitive coupling of the electrode 271with the free space is weakened, and capacitive coupling of theelectrode 271 with the communication medium 280 becomes dominant. Whenthe communication medium 280 is a conductor or an object having a higherdielectric constant than air, a capacitance Cte 294 viewed from theelectrode 271 is larger than the capacitance Ctg 295. Hence, when somesignal is supplied to the electrodes, the magnitude of a load attachedto the paths is known on the basis of the magnitude of signal level ofthe load. In the case of the free space, the capacitance is low, andthus the signal level of the load is low. In the case of a conductor ora dielectric, the capacitance is high, and thus the signal level of theload is higher.

The capacitance as viewed from the electrode is thus changed, andthereby the signal level (magnitude of amplitude) detected when a signalis applied to the electrode is changed. Thus, by detecting the signallevel, the electrode controlling unit 261 can grasp a state of theelectrode (whether the communication medium 280 is in the vicinity ornot). The electrode controlling unit 261 controls the connection betweenthe transmitting unit 263 and the electrode unit 262 according to thestate of each electrode which state is thus grasped.

The transmitting unit 263 connects each of the electrode 271 and theelectrode 272 of the electrode unit 262 as the transmission signalelectrode or the transmission reference electrode under control of theelectrode controlling unit 261.

FIG. 8 is a block diagram showing an example of detailed configurationof the electrode controlling unit 261 in FIG. 7. The electrodecontrolling unit 261 in FIG. 8 has a main control unit 301, a signalinput controlling unit 302, a retaining unit 303, a connectioncontrolling unit 304, a switching controlling unit 305, a signal source311, a switch 312, a detecting unit 313, and a connecting unit 314.

The main control unit 301 performs a process of controlling theconnection between the electrode unit 262 and the transmitting unit 263by controlling various parts within the electrode controlling unit 261,for example the signal input controlling unit 302, the retaining unit303, the connection controlling unit 304, and the switching controllingunit 305. The signal input controlling unit 302 is controlled by themain control unit 301 to turn on or off the switch 312. The signal inputcontrolling unit 302 thereby controls input of a signal generated in thesignal source 311 to each electrode of the electrode unit 262.

The retaining unit 303 is controlled by the main control unit 301 toretain a signal level detected in the detecting unit 313 and supply thevalue to the main control unit 301 as required. The connectioncontrolling unit 304 is controlled by the main control unit 301 tocontrol the switching of connection by the connecting unit 314. Theswitching controlling unit 305 is controlled by the main control unit301 to supply information for controlling the connection between theelectrode unit 262 and the transmitting unit 263 to the transmittingunit 263. The switching controlling unit 305 thereby controls theconnection between the electrode unit 262 and the transmitting unit 263.

The signal source 311 supplies a signal of a predetermined frequency tothe switch 312. The switch 312 is controlled by the signal inputcontrolling unit 302 to supply the signal from the signal source 311 tothe detecting unit 313, or to stop the supply. The detecting unit 313has a load resistance 321 having a predetermined resistance value withinthe detecting unit 313. The detecting unit 313 can detect a potentialacross the load resistance 321. That is, information on the potentialacross the load resistance 321 is supplied to the retaining unit 303.The retaining unit 303 obtains a signal level applied to an electrode onthe basis of the information on the potential across the load resistance321, and retains the value.

The connecting unit 314 has a kind of multi-contact switch. Themulti-contact switch changes connection between a terminal 322 connectedto the detecting unit 313 and a plurality of terminals provided for eachelectrode. In the case of FIG. 8, for example, the terminal 323 isconnected to the electrode 271, and the terminal 324 is connected to theelectrode 272. That is, the connecting unit 314 is controlled by theconnection controlling unit 304 to perform switching so as to connectthe terminal 322 to the terminal 323 or the terminal 324 or not toconnect the terminal 322 to the terminal 323 or the terminal 324. Theconnecting unit 314 thereby performs switching so as to supply thesignal from the signal source 311 to the electrode 271 or the electrode272, or not to supply the signal from the signal source 311 to theelectrode 271 or the electrode 272.

In a mode of checking capacitive coupling of each electrode, the maincontrol unit 301 controls the connection controlling unit 304 tosequentially connect the terminal 322 in the connecting unit 314 to eachof the terminal 323 and the terminal 324, and finally release theconnection and set an open state. In addition, the main control unit 301controls the signal input controlling unit 302 in each of these states(the state of the terminal 322 being connected to the terminal 323, thestate of the terminal 322 being connected to the terminal 324, and thestate of the terminal 322 being unconnected), so that the switch isturned on for a predetermined time to apply the signal. The detectingunit 313 detects the signal level of each signal thus applied, and thensupplies the signal level to the retaining unit 303 to make the signallevel retained by the retaining unit 303. When obtaining the result ofdetection of the signal level from the retaining unit 303, the maincontrol unit 301 supplies the result of detection of the signal level ascontrol information to the transmitting unit 263 via the switchingcontrolling unit 305.

FIG. 9 is a block diagram showing an example of detailed configurationof the transmitting unit 263 in FIG. 7.

The transmitting unit 263 in FIG. 9 has a transmission controlling unit351, a transmission signal generating unit 352, an amplifying unit 353,a connecting unit 354, and a connection controlling unit 355.

The transmission controlling unit 351 controls each part within thetransmitting unit 263 to thereby perform a control process for signaltransmission, such as controlling connection to the electrode unit 262and outputting a transmission signal, on the basis of the controlinformation supplied from the electrode controlling unit 261 (theswitching controlling unit 305 in the electrode controlling unit 261).

The transmission signal generating unit 352 can generate a plurality ofkinds of transmission signals, for example. The transmission signalgenerating unit 352 generates a transmission signal corresponding totransmission information indicated by the transmission controlling unit351, and then supplies the transmission signal to the amplifying unit353. The amplifying unit 353 is formed by an operational amplifier orthe like. Under control of the transmission controlling unit 351, theamplifying unit 353 amplifies the transmission signal supplied from thetransmission signal generating unit 352, and then supplies thetransmission signal to the connecting unit 354 to supply thetransmission signal to the transmission signal electrode and thetransmission reference electrode. The connecting unit 354 has amulti-contact switch for switching connection between output terminalsof the amplifying unit 353 and electrodes. That is, under control of theconnection controlling unit 355, the connecting unit 354 connects eachof the output terminal 361 and the output terminal 362 of the amplifyingunit 353 to one of a terminal 363 and a terminal 364 (terminalsdifferent from each other), or disconnect (open) both the outputterminal 361 and the output terminal 362. In the example of FIG. 9, theconnecting unit 354 connects the output terminal 361 of the amplifyingunit 353 for the transmission signal electrode to the terminal 364(electrode 272), and connects the output terminal 362 for thetransmission reference electrode to the terminal 363 (electrode 271).That is, in this case, the electrode 271 acts as the transmissionreference electrode, and the electrode 272 acts as the transmissionsignal electrode.

For example, in a mode of transmitting a signal, on the basis of thecontrol information generated and supplied by the electrode controllingunit 261 in the mode of checking the capacitive coupling of eachelectrode, the transmission controlling unit 351 controls the connectioncontrolling unit 355 to connect each terminal of the connecting unit 354and thereby determine the transmission signal electrode and thetransmission reference electrode. When the connection to the electrodeunit 262 is established, the transmission controlling unit 351 controlsthe transmission signal generating unit 352 to generate a transmissionsignal, controls the amplifying unit 353 to amplify the transmissionsignal, and then makes the transmission signal output from the electrodeunit 262 to the communication medium 280 via the connecting unit 354.

As described above, the transmitting device 260 performs optimization byswitching the transmission signal electrode and the transmissionreference electrode according to a state of capacitive coupling of eachelectrode, and then transmits a signal. Therefore the signal can betransmitted to the receiving device stably irrespective of positionalrelation to the human body of a user as communication medium.

A flow of a process for such control of the electrodes will next bedescribed. First, a flow of an electrode controlling process in atransmission process performed by the transmitting device 260 will bedescribed with reference to a flowchart of FIG. 10.

While the transmission process is performed, the main control unit 301in step S1 controls the transmission controlling unit 351 in thetransmitting unit 263 via the switching controlling unit 305 to stoptransmitting a signal, with predetermined timing or a predeterminedprocess as a cue. According to an instruction from the main control unit301, the transmission controlling unit 351 controls the transmissionsignal generating unit 352 to stop generating the signal.

When the generation of the signal is stopped, the main control unit 301advances the process to step S2, where the main control unit 301performs the electrode controlling process for controlling theconnection between the electrode unit 262 and the transmitting unit 263.Details of the electrode controlling process will be described later.When the electrode controlling process is ended, the main control unit301 advances the process to step S3, where the main control unit 301controls the transmission controlling unit 351 in the transmitting unit263 via the switching controlling unit 305 to start transmitting asignal. According to an instruction from the main control unit 301, thetransmission controlling unit 351 controls the transmission signalgenerating unit 352 to start generating the signal.

When the transmission of the signal is ended, the main control unit 301ends the transmission process.

As described above, the signal is transmitted, and optimization isperformed by switching the transmission signal electrode and thetransmission reference electrode according to a state of capacitivecoupling of each electrode. Therefore the main control unit 301 cantransmit the signal to the receiving device stably irrespective ofpositional relation between the transmitting device 260 and thecommunication medium 280.

Details of the electrode controlling process performed in step S2 inFIG. 10 will next be described with reference to a flowchart of FIG. 11.

When the electrode controlling process is started, the main control unit301 in step S21 controls the transmitting unit 263 via the switchingcontrolling unit 305 to disconnect the electrodes and the transmittingunit from each other. Under the control, the transmission controllingunit 351 in the transmitting unit 263 makes each terminal of theconnecting unit 354 opened, thereby disconnecting the electrode unit 262and the transmitting unit 263 from each other.

After each electrode and the transmitting unit 263 are disconnected fromeach other, the main control unit 301 in step S22 controls theconnecting unit 314 via the connection controlling unit 304 to set theconnection between the electrode unit 262 and the electrode controllingunit 261 to an initial value. That is, the main control unit 301controls the connecting unit 314 to connect the electrode to be checkedfirst to the detecting unit 313. Then, the main control unit 301 in stepS23 controls the signal input controlling unit 302 to set the switch 312in an on state, whereby a signal generated in the signal source 311 isinput to the detecting unit 313. The signal is supplied to an electrodeof the electrode unit 262 via the detecting unit 313 and the connectingunit 314. The detecting unit 313 in step S24 detects a potentialdifference across the load resistance 321 as a signal level, andsupplies information on the potential difference to the retaining unit303. The retaining unit 303 in step S25 retains the information on thepotential difference as signal level.

In step S26, the main control unit 301 determines whether the signallevel is detected in all patterns. When the main control unit 301determines that the detection is completed, the main control unit 301advances the process to step S27, where the main control unit 301obtains the detected signal level from the retaining unit 303, andselects each of the electrodes of the electrode unit 262 as an electrodeto be used as the transmission signal electrode or as an electrode to beused as the transmission reference electrode on the basis of theobtained signal level. For example, when the signal level is apredetermined threshold value or higher, the capacitance formed betweenthe electrode and the surroundings is large, and therefore the maincontrol unit 301 determines that the communication medium 280 is inproximity, and selects the electrode as the transmission signalelectrode. Conversely, for example, when the signal level is lower thanthe predetermined threshold value, the capacitance formed between theelectrode and the surroundings is small, and therefore the main controlunit 301 determines that the electrode is capacitively coupled with thespace, and selects the electrode as the transmission referenceelectrode.

The main control unit 301 in step S28 controls the connecting unit 314via the connection controlling unit 304 to open all the terminals andthereby disconnect the electrode unit 262 and the electrode controllingunit 261 from each other. Then, the main control unit 301 suppliesidentifying information for the transmission signal electrode and thetransmission reference electrode which information indicates whichelectrode is to be used as the transmission signal electrode or thetransmission reference electrode to the transmission controlling unit351 in the transmitting unit 263 via the switching controlling unit 305.The transmission controlling unit 351 in step S29 controls theconnecting unit 354 to connect the electrodes of the electrode unit 262to the transmitting unit 263 on the basis of the supplied identifyinginformation. That is, the electrode unit 262 is thereby connected to thetransmitting unit 263 by a method optimized on the basis of checks bythe electrode controlling unit 261. When the process of step S29 isended, the main control unit 301 ends the electrode controlling process.

Incidentally, when the main control unit 301 determines in step S26 thatthe signal level is not detected in all the patterns (signal levels forall the electrodes are not detected), the main control unit 301 in stepS30 controls the connecting unit 314 via the connection controlling unit304 to reset a pattern of connection between the electrode unit 262 andthe electrode controlling unit 261. That is, the connecting unit 314connects the terminal 322 connected to the detecting unit 313 to theterminal for the electrode to be checked next. After the process of stepS30 is ended, the main control unit 301 returns the process to step S23to perform the process for the new electrode.

That is, each part of the electrode controlling unit 261 repeatedlyperforms the processes of steps S23 to S26 and step S30 to check a stateof capacitive coupling of each electrode. When the checking of all theelectrodes is thereafter ended, the main control unit 301 performs theprocess from step S27 on down to optimize the connection between theelectrode unit 262 and the transmitting unit 263.

Because the electrode controlling process is performed as describedabove, the main control unit 301 can determine for each of theelectrodes whether to use the electrode as the transmission referenceelectrode or whether to use the electrode as the transmission signalelectrode, and a signal can be transmitted to the receiving devicestably irrespective of the positional relation between the transmittingdevice 260 and the communication medium 280.

Incidentally, there may be three or more electrodes in the electrodeunit 262. In this case, the transmitting device 260 can controlselection of an electrode pair by switching the connecting unit 354.That is, in this case, the transmitting device 260 does not need todetermine an electrode to be used as the transmission signal electrodeand an electrode to be used as the transmission reference electrode insuch a manner as to distinguish the electrodes from each other; itsuffices to determine which plurality of electrodes among the group ofelectrodes of the electrode unit 262 are to be used as a pair of thetransmission signal electrode and the transmission reference electrode.That is, in this case, of the electrodes connected to the outputterminal 361 and the output terminal 362, the electrode nearer to thecommunication medium 280 acts as the transmission signal electrode as aconsequence, and the electrode more distant from the communicationmedium 280 acts as the transmission reference electrode as aconsequence. Therefore the output terminal for the transmissionreference electrode and the output terminal for the transmission signalelectrode do not need to be differentiated from each other.

In addition, the transmitting device 260 may specify and use a pluralityof electrodes as the transmission signal electrode, and specify and usea plurality of electrodes as the transmission reference electrode. Inaddition, the transmitting device 260 may specify electrodes to be usedas the transmission signal electrode and electrodes to be used as thetransmission reference electrode such that the electrodes to be used asthe transmission signal electrode and the electrodes to be used as thetransmission reference electrode are different from each other innumber.

While the transmitting device has been described above, the presentinvention can be similarly adapted to the receiving device correspondingto the transmitting device. That is, the receiving device can alsochange (control) connection between electrodes and an internal circuitsuch that positional relation between the received signal electrode andthe reception reference electrode and the communication medium isoptimized according to positional relation between the receiving deviceand the communication medium. Hence, the description of the electrodeconnection control in the transmitting device described above withreference to FIG. 6 can be applied to the receiving device. In addition,arrangement relation of the electrodes is arbitrary. Further, themagnitudes of surface areas and shapes of the electrodes are arbitrary,and may be different from each other, of course.

FIG. 12 is a block diagram showing an example of internal configurationof an embodiment of such a receiving device.

A receiving device 370 in FIG. 12 corresponds to the transmitting device260, and receives a signal supplied by the transmitting device 260 viathe communication medium 280. The receiving device 370 mainly has anelectrode controlling unit 371, an electrode unit 372, and a receivingunit 373.

The electrode controlling unit 371 is a processing unit corresponding tothe electrode controlling unit 261 in the transmitting device 260 shownin FIG. 7. The electrode controlling unit 371 controls connectionbetween the receiving unit 373 and the electrode unit 372. Specifically,the electrode controlling unit 371 checks a state of capacitive couplingof each electrode in the electrode unit 372, identifies the electrode tobe used as received signal electrode and the electrode to be used asreception reference electrode, and then supplies identifying informationidentifying the electrodes as control information to the receiving unit373. The electrode controlling unit 371 has basically the sameconfiguration and operation as the electrode controlling unit 261. Thedescription above made with reference to FIG. 7 and the block diagramand the description of the electrode controlling unit 261 shown in FIG.8 can be applied to the electrode controlling unit 371, and thereforedescription thereof will be omitted.

The electrode unit 372 corresponds to the electrode unit 262 in thetransmitting device 260 shown in FIG. 7. As with the electrode unit 262,the electrode unit 372 has an electrode 381 and an electrode 382 as apair of electrodes having the shape of a disk, for example, andcapacitively coupled with an outside. The receiving unit 373 correspondsto the transmitting unit 263 in the transmitting device 260 shown inFIG. 7. The receiving unit 373 performs a process of receiving a signalvia the electrode unit 372 instead of the transmission process.

For example, suppose that as shown in FIG. 12, the communication medium280 serving as a communication path and having conductivity ordielectric properties approaches the electrode 381. At this time, theelectrode 382 is facing a free space, and forms a capacitance Crg 395with the free space. On the other hand, as the communication medium 280approaches the electrode 381, capacitive coupling of the electrode 381with the free space is weakened, and capacitive coupling of theelectrode 381 with the communication medium 280 becomes dominant. Whenthe communication medium 280 is a conductor or an object having a higherdielectric constant than air, a capacitance Cre 394 viewed from theelectrode 381 is larger than the capacitance Crg 395. Hence, when somesignal is supplied to the electrodes, the magnitude of a load attachedto the paths is known on the basis of the magnitude of signal level ofthe load. In the case of the free space, the capacitance is low, andthus the signal level of the load is low. In the case of a conductor ora dielectric, the capacitance is high, and thus the signal level of theload is higher.

The capacitance as viewed from the electrode is thus changed, andthereby the signal level (magnitude of amplitude) detected when a signalis applied to the electrode is changed. Thus, as with electrodecontrolling unit 261, by detecting the signal level, the electrodecontrolling unit 371 can grasp a state of the electrode (whether thecommunication medium 280 is in the vicinity or not). The electrodecontrolling unit 371 controls the connection between the receiving unit373 and the electrode unit 372 according to the state of each electrodewhich state is thus grasped.

Incidentally, the pattern of connection of the terminals in theconnecting unit 354 shown in FIG. 9 is an example of connection. Inpractice, the connecting unit 354 is controlled by the connectioncontrolling unit 355 as described above to change the connection of eachterminal in a plurality of connection patterns including a connectionpattern shown in FIG. 13.

FIG. 13 is a block diagram showing an example of detailed configurationof the receiving unit 373. The receiving unit 373 in FIG. 13 has areception controlling unit 401, a connection controlling unit 402, aconnecting unit 403, an amplifying unit 404, and a received signalobtaining unit 405.

On the basis of the control information supplied from the electrodecontrolling unit 371 (identifying information identifying the electrodeto be used as the received signal electrode and the electrode to be usedas the reception reference electrode in the electrode group of theelectrode unit 372), the reception controlling unit 401 controls theconnecting unit 403 via the connection controlling unit 402 to connect aterminal 413 connected to a terminal of the amplifying unit 404 for thereceived signal electrode to the received signal electrode, and connecta terminal 414 connected to a terminal of the amplifying unit 404 forthe reception reference electrode to the reception reference electrode.In the case of FIG. 13, the connecting unit 403 connects the terminal413 to a terminal 412 connected to the electrode 382, and connects theterminal 414 to a terminal 411 connected to the electrode 381. That is,in this case, the electrode 381 is connected so as to act as thereceived signal electrode, and the electrode 382 is connected so as toact as the reception reference electrode.

In addition, the reception controlling unit 401 controls the amplifyingunit 404 as required to amplify a received signal and then supply thereceived signal to the received signal obtaining unit 405, and controlsthe received signal obtaining unit 405 as required to obtain theamplified received signal.

As described above, the receiving device 370 controls the electrodes inthe same manner as the transmitting device 260. That is, the receivingdevice 370 performs a reception process in a similar manner to thetransmission process shown in the flowchart of FIG. 10. The receivingdevice 370 stops signal reception, and then performs the electrodecontrolling process. After the electrode controlling process is ended,the receiving device 370 resumes signal reception. The receiving device370 performs an electrode controlling process as in the case of theelectrode controlling process represented in the flowchart of FIG. 11.The receiving device 370 inputs a signal to each electrode, grasps astate of capacitive coupling of each electrode on the basis of a signallevel obtained, and then determines the received signal electrode andthe reception reference electrode.

As described above, the signal is received, and optimization isperformed by switching the received signal electrode and the receptionreference electrode according to the state of the capacitive coupling ofeach electrode. Therefore the reception controlling unit 401 enables asignal transmitted from the transmitting device to be received stablyirrespective of positional relation between the receiving device 370 andthe communication medium 280.

Incidentally, the electrode controlling process may be performed whilethe transmitting device 260 and the receiving device 370 performingcommunication are synchronized with each other. A flow of the process inthis case will be described with reference to a flowchart of FIG. 14.

The transmitting device 260 that has been performing the transmissionprocess first transmits a transmission stop notifying signal to thereceiving device 370 in step S41 to notify the receiving device 370 thatthe transmission process will be stopped. When the notification iscompleted, the transmitting device 260 advances the process to step S42,where the transmitting device 260 stops signal transmission. Thetransmitting device 260 performs the electrode controlling processdescribed with reference to the flowchart of FIG. 11 in step S43.

When the receiving device 370 in step S61 receives the transmission stopnotifying signal transmitted in step S41 by the transmitting device 260,the receiving device 370 advances the process to step S62, whereby thereceiving device 370 stops signal reception. The receiving device 370thereafter performs the electrode controlling process described withreference to the flowchart of FIG. 11 in step S63.

After the electrode controlling process in step S43 is ended, and thusthe connection between the electrode unit 262 and the transmitting unit263 is optimized, the transmitting device 260 advances the process tostep S44, where the transmitting device 260 starts signal transmission.Then the process is ended.

After the receiving device 370 ends the electrode controlling process,and thus optimizes the connection between the electrode unit 372 and thereceiving unit 373, the receiving device 370 advances the process tostep S64, where the receiving device 370 starts signal reception. Thenthe process is ended.

As described above, the transmitting device 260 and the receiving device370 synchronize timing of performing the electrode controlling processwith each other. Thereby, the transmitting device 260 and the receivingdevice 370 reduce problems in communication such for example as a casewhere the transmitting device 260 transmits a signal while the receivingdevice 370 is performing the electrode controlling process. Thereforethe communication process can be performed more efficiently and moreaccurately.

Incidentally, while in the above description, the electrode unit 372 hastwo electrodes (the electrode 381 and the electrode 382), the presentinvention is not limited to this, and the number of such electrodes maybe three or more. In this case, the receiving device 370 can controlselection of an electrode pair by switching the connecting unit 403.That is, in this case, the receiving device 370 does not need todetermine an electrode to be used as the received signal electrode andan electrode to be used as the reception reference electrode in such amanner as to distinguish the electrodes from each other; it suffices todetermine which plurality of electrodes among the group of electrodes ofthe electrode unit 372 are to be used as a pair of the received signalelectrode and the reception reference electrode. That is, in this case,of the electrodes connected to the input terminal 413 and the inputterminal 414, the electrode nearer to the communication medium 280 actsas the received signal electrode as a consequence, and the electrodemore distant from the communication medium 280 acts as the receptionreference electrode as a consequence. Therefore the output terminal forthe reception reference electrode and the output terminal for thereceived signal electrode do not need to be differentiated from eachother. In addition, arrangement relation of the electrodes is arbitrary.Further, the magnitudes of surface areas and shapes of the electrodesare arbitrary, and may be different from each other, of course.

In addition, the receiving device 370 may specify and use a plurality ofelectrodes as the received signal electrode, and specify and use aplurality of electrodes as the reception reference electrode. Inaddition, the receiving device 370 may specify electrodes to be used asthe received signal electrode and electrodes to be used as the receptionreference electrode such that the electrodes to be used as the receivedsignal electrode and the electrodes to be used as the receptionreference electrode are different from each other in number.

Incidentally, one device may of course have both the functions of theabove-described transmitting device 260 and the functions of thereceiving device 370.

FIG. 15 is a block diagram showing an example of configuration of anembodiment of a communicating device to which the present invention isapplied, the communicating device corresponding to the transmittingdevice 260 in FIG. 7 and the receiving device 370 in FIG. 13.

The communicating device 450 in FIG. 15 performs the same communicationsas the communications performed by the transmitting device 260 and thereceiving device 370 bidirectionally with another communicating device450 via a communication medium 280. The communicating device 450 has anelectrode controlling unit 451, an electrode unit 452, and acommunicating unit 453.

The electrode controlling unit 451 is a processing unit corresponding tothe electrode controlling unit 261 (FIG. 7) and the electrodecontrolling unit 371 (FIG. 12). The electrode controlling unit 451controls connection between the electrode unit 452 and the communicatingunit 453. Specifically, the electrode controlling unit 451 checks astate of capacitive coupling of each electrode in the electrode unit452, identifies an electrode to be used as transmission signalelectrode, an electrode to be used as received signal electrode, anelectrode to be used as transmission reference electrode, and anelectrode to be used as reception reference electrode, and then suppliesidentifying information identifying the electrodes as controlinformation to the communicating unit 453. The electrode controllingunit 451 has basically the same configuration and operation as theelectrode controlling unit 261 and the electrode controlling unit 371.The block diagram and the description of the electrode controlling unit261 shown in FIG. 8 can be applied to the electrode controlling unit451, and therefore description thereof will be omitted. However, sincethe electrode unit 452 has four electrodes, the electrode controllingunit 451 checks states of capacitive coupling of all the fourelectrodes. More specifically, while the connecting unit 314 in FIG. 8has been described as a switch having two contacts on one side whichswitch selectively connects the terminal 322 to the terminal 323 or theterminal 324, because the number of terminals selected to be connectedto the terminal 322 corresponds to the number of electrodes in theelectrode unit, the connecting unit in the communicating device 450 isformed by a switch having four contacts on one side.

The electrode unit 452 corresponds to the electrode unit 262 in thetransmitting device 260 shown in FIG. 7. As with the electrode unit 262,the electrode unit 452 has pairs of electrodes having the shape of adisk, for example, and capacitively coupled with an outside. However,the electrode unit 452 has four electrodes 461 to 464. The communicatingunit 453 corresponds to the transmitting unit 263 in the transmittingdevice 260 shown in FIG. 7. The communicating unit 453 performs not onlya transmission process but also a process of receiving a signal via theelectrode unit 452. That is, the electrode unit 452 performs acommunication process for achieving a two-way communication with anothercommunicating device 450.

For example, suppose that as shown in FIG. 15, the communication medium280 serving as a communication path and having conductivity ordielectric properties approaches the electrode 461 and the electrode462. At this time, the electrode 463 is facing a free space, and forms acapacitance Ccg 473 with the free space (a capacitance between theelectrode 463 and a reference point 496-1 representing a virtual pointat infinity from the electrode 463). Similarly, the electrode 464 isalso facing the free space, and forms a capacitance Ccg 474 with thefree space (a capacitance between the electrode 464 and a referencepoint 496-2 representing a virtual point at infinity from the electrode464). On the other hand, as the communication medium 280 approaches theelectrode 461 and the electrode 462, capacitive coupling of theelectrode 461 and the electrode 462 with the free space is weakened, andcapacitive coupling of the electrode 461 and the electrode 462 with thecommunication medium 280 becomes dominant. When the communication medium280 is a conductor or an object having a higher dielectric constant thanair, a capacitance Cce 471 viewed from the electrode 461 and acapacitance Cce 472 viewed from the electrode 462 are larger than thecapacitance Ccg 473 or Ccg 474. Hence, when some signal is supplied tothe electrodes, the magnitude of a load attached to the paths is knownon the basis of the magnitude of signal level of the load. In the caseof the free space, the capacitance is low, and thus the signal level ofthe load is low. In the case of a conductor or a dielectric, thecapacitance is high, and thus the signal level of the load is higher.

The capacitance as viewed from the electrode is thus changed, andthereby the signal level (magnitude of amplitude) detected when a signalis applied to the electrode is changed. Thus, by detecting the signallevel, the electrode controlling unit 451 can grasp a state of theelectrode (whether the communication medium 280 is in the vicinity ornot). The electrode controlling unit 451 controls the connection betweenthe communicating unit 453 and the electrode unit 452 according to thestate of each electrode which state is thus grasped.

Under control of the electrode controlling unit 451, the communicatingunit 453 connects each of the electrodes 461 to 464 of the electrodeunit 452 as the transmission signal electrode, the transmissionreference electrode, the received signal electrode, or the receptionreference electrode, or does not connect each of the electrodes 461 to464.

Incidentally, the pattern of connection of the terminals in theconnecting unit 403 shown in FIG. 13 is an example of connection. Inpractice, the connecting unit 403 is controlled by the connectioncontrolling unit 402 as described above to change the connection of eachterminal in a plurality of connection patterns including the connectionpattern shown in FIG. 13.

FIG. 16 is a block diagram showing an example of detailed configurationof the communicating unit 453 in FIG. 15. As shown in FIG. 16, thecommunicating unit 453 has a communication controlling unit 501, atransmission signal generating unit 502, an amplifying unit 503, aconnection controlling unit 504, a connecting unit 505, an amplifyingunit 506, and a received signal obtaining unit 507.

That is, for two-way communication, the communicating unit 453 has botha configuration corresponding to the transmitting unit 263 in FIG. 9 anda configuration corresponding to the receiving unit 373 shown in FIG.13. Specifically, the communication controlling unit 501 corresponds tothe transmission controlling unit 351 in FIG. 9 and the receptioncontrolling unit 401 in FIG. 13. The communication controlling unit 501performs a control process involved in a transmission process and areception process on the basis of control information supplied from theelectrode controlling unit 451. The transmission signal generating unit502 corresponds to the transmission signal generating unit 352 in FIG.9. The transmission signal generating unit 502 is controlled by thecommunication controlling unit 501 to generate a transmission signalcorresponding to transmission information, and supply the transmissionsignal to the amplifying unit 503. The amplifying unit 503 correspondsto the amplifying unit 353 in FIG. 9. The amplifying unit 503 iscontrolled by the communication controlling unit 501 to amplify thetransmission signal supplied from the transmission signal generatingunit 502, and supply the amplified transmission signal to the connectingunit 505.

The connection controlling unit 504 corresponds to the connectioncontrolling unit 355 in FIG. 9 and the connection controlling unit 402in FIG. 13. The connection controlling unit 504 is controlled by thecommunication controlling unit 501 to control connections in theconnecting unit 505. The connecting unit 505 corresponds to theconnecting unit 354 in FIG. 9 and the connection controlling unit 402 inFIG. 13. The connecting unit 505 controls connections between theamplifying unit 503 and the amplifying unit 506 and the electrodes 461to 464. The connecting unit 505 has a terminal 511 connected to aterminal of the amplifying unit 503 for the transmission signalelectrode, a terminal 512 connected to a terminal of the amplifying unit503 for the transmission reference electrode, a terminal 531 connectedto a terminal of the amplifying unit 506 for the received signalelectrode, and a terminal 532 connected to a terminal of the amplifyingunit 506 for the reception reference electrode. The connecting unit 505connects each of these terminals to one of a terminal 521 connected tothe electrode 461, a terminal 522 connected to the electrode 462, aterminal 523 connected to the electrode 463, and a terminal 524connected to the electrode 464 (terminals different from each other).That is, the connecting unit 505 performs a process of assigning theelectrodes 461 to 464 as one of the transmission signal electrode, thetransmission reference electrode, the received signal electrode, and thereception reference electrode.

The amplifying unit 506 corresponds to the amplifying unit 404 in FIG.13. The amplifying unit 506 is controlled by the communicationcontrolling unit 501 to amplify a received signal supplied via theconnecting unit 505 and supply the received signal to the receivedsignal obtaining unit 507. The received signal obtaining unit 507corresponds to the received signal obtaining unit 405 in FIG. 13. Thereceived signal obtaining unit 507 is controlled by the communicationcontrolling unit 501 to obtain the received signal supplied from theamplifying unit 506.

Since the electrode controlling process is performed as described above,the communicating device 450 can determine for each of the electrodeswhether to use the electrode as the transmission reference electrode,whether to use the electrode as the transmission signal electrode,whether to use the electrode as the reception reference electrode,whether to use the electrode as the received signal electrode, orwhether to disconnect the electrode. The communicating device 450 cantherefore perform signal transmission and reception stably irrespectiveof positional relation between the communicating device 450 and thecommunication medium 280.

Incidentally, there may be five or more electrodes in the electrode unit452. In this case, the communicating device 450 can control selection ofan electrode pair by switching the connecting unit 505. That is, in thiscase, the communicating device 450 does not need to determine anelectrode to be used as the transmission signal electrode and anelectrode to be used as the transmission reference electrode in such amanner as to distinguish the electrodes from each other, and does notneed to determine an electrode to be used as the received signalelectrode and an electrode to be used as the reception referenceelectrode in such a manner as to distinguish the electrodes from eachother. It suffices for the communicating device 450 to determine whichplurality of electrodes or which electrode among the group of electrodesof the electrode unit 452 are to be used as an electrode pair for signaltransmission, and determine which plurality of electrodes or whichelectrode among the group of electrodes of the electrode unit 452 are tobe used as an electrode pair for signal reception.

In addition, the communicating device 450 may allow an electrode to beshared between the electrode pair for signal transmission and theelectrode pair for signal reception. Further, the communicating device450 may identify a plurality of electrodes as electrodes to be used asthe transmission signal electrode, identify a plurality of electrodes aselectrodes to be used as the transmission reference electrode, identifya plurality of electrodes as electrodes to be used as the receivedsignal electrode, and identify a plurality of electrodes as electrodesto be used as the reception reference electrode.

In addition, the communicating device 450 may identify electrodes to beused as the transmission signal electrode, electrodes to be used as thetransmission reference electrode, electrodes to be used as the receivedsignal electrode, and electrodes to be used as the reception referenceelectrode such that the electrodes to be used as the transmission signalelectrode, the electrodes to be used as the transmission referenceelectrode, the electrodes to be used as the received signal electrode,and the electrodes to be used as the reception reference electrode aredifferent from each other in number. In addition, arrangement relationof the electrodes is arbitrary. Further, the magnitudes of surface areasand shapes of the electrodes are arbitrary, and may be different fromeach other, of course.

Incidentally, the pattern of connection of the terminals in theconnecting unit 505 shown in FIG. 16 is an example of connection. Inpractice, the connecting unit 505 is controlled by the connectioncontrolling unit 504 as described above to change the connection of eachterminal in a plurality of connection patterns including a connectionpattern shown in FIG. 16.

Incidentally, the communicating device 450 performs a transmissionprocess and a reception process in the same manner as the transmittingdevice 260 and the receiving device 370 described above. Hence, thecommunicating device 450 performs the electrode controlling process ofchecking a state of capacitive coupling of each electrode and assigningeach electrode as one of the transmission signal electrode, thetransmission reference electrode, the received signal electrode, and thereception reference electrode according to the state in the same manneras described with reference to the flowchart of FIG. 11. Thereforedescription thereof will be omitted.

Incidentally, a plurality of communicating devices 450 performingcommunication may synchronize timing of performing the electrodecontrolling process as in the case of the transmitting device 260 andthe receiving device 370 described above. A flow of the process in thiscase will be described with reference to a flowchart of FIG. 17.

With predetermined timing or a predetermined event as a cue, one of twocommunicating devices 450 communicating with each other (a communicatingdevice 450-1) transmits a transmission and reception stop notifyingsignal notifying a stoppage of a transmission and reception process tothe other communicating device in step S81. The other communicatingdevice 450-2 as the other device communicating with the communicatingdevice 450-1 receives the transmission and reception stop notifyingsignal in step S101. The communicating device 450-2 transmits anacknowledgment signal in response to the received transmission andreception stop notifying signal in step S102.

The communicating device 450-1 receives the acknowledgment signal instep S82. Receiving the acknowledgment signal, the communicating device450-1 stops signal transmission and reception in step S83, and performsthe electrode controlling process in step S84. Details of the electrodecontrolling process are the same as described with reference to theflowchart of FIG. 11, and therefore description thereof will be omitted.After the electrode controlling process is ended, the communicatingdevice 450-1 starts signal transmission and reception in step S85, andthen ends the process.

The communicating device 450-2 that has transmitted the acknowledgmentsignal stops signal transmission and reception in step S103, andperforms the electrode controlling process in step S104. Details of theelectrode controlling process are the same as described with referenceto the flowchart of FIG. 11, and therefore description thereof will beomitted. After the electrode controlling process is ended, thecommunicating device 450-2 starts signal transmission and reception instep S105, and then ends the process.

As described above, the communicating device 450-1 and the communicatingdevice 450-2 performing communication synchronize the timing ofperforming the electrode controlling process with each other. Thereby,the communicating devices 450 reduce problems in communication such forexample as a case where while one of the communicating devices 450 isperforming the electrode controlling process, the other device transmitsa signal. Therefore the communication process can be performed moreefficiently and more accurately.

For the determination of the detecting unit in each device describedabove, a method can be considered in which method a comparison signallevel is determined in advance, and determination is made on the basisof whether a signal level is higher or lower than the comparison signallevel. The electrode whose level is close to the comparison signal levelmay be in a subtle position relation to the communication medium 30 (forexample the hand 220 in FIG. 6), and therefore is not connected to anyelectrode by the connecting unit of the transmitting device, thereceiving device, and the communicating device, whereby adverse effectson other electrodes can be avoided.

Incidentally, the timing of performing the electrode controlling processdescribed above (that is, updating the function assigned to eachelectrode) may be any timing. For example, however, when thecommunicating device 450 is formed as a mobile device or the like, andcommunication is performed with a human body (user) as a communicationmedium, positional relation between the user (communication medium) andthe communicating device 450 (electrodes) may be changed during thecommunication as a result of for example the user changing a manner ofholding the communicating device 450. It is therefore desirable not onlyto perform the electrode controlling process in an initial state at atime of a start or the like but also to repeatedly perform the electrodecontrolling process at a predetermined frequency during communication.

For example, as shown in FIG. 18A, the communicating device 450 mayperform the electrode controlling process (control 551 or control 554)using a free time during which the transmission process (transmission552) or the reception process (reception 553 or reception 555) is notperformed (when the transmission process or the reception process is notperformed for a predetermined time, for example), and thereby update theassignment of electrodes as the transmission signal electrode, thetransmission reference electrode, the received signal electrode, or thereception reference electrode. Thus, the communicating device 450 canperform communication while using time effectively, and thereby improvecommunication efficiency.

In addition, for example, as shown in FIG. 18B, the communicating device450 may continuously perform the electrode controlling process, thetransmission process, and the reception process such as control 561,transmission 562, reception 563, control 564, transmission 565, andreception 566, and repeatedly perform the processes as one cycle. Forexample, in the example shown in FIG. 18B, the communicating device 450continuously performs the electrode controlling process, thetransmission process, and the reception process in respective T/3 timeswith a periodic T time as a repetition period, and further repeatedlyperforms the series of processes as one cycle. Thus, timing ofperforming each process is fixed. Therefore the communicating device 450can easily synchronize the timing of the performance with anothercommunicating device 450.

Further, as shown in FIG. 18C, for example, the communicating device 450may perform the electrode controlling process using a transmissionsignal. In this case, the transmission process (transmission 571 ortransmission 574) and the electrode controlling process (control 572 orcontrol 575) are performed simultaneously. The reception process(reception 573 or reception 576) is performed in other times. In thiscase, the communicating device 450 measures a signal level whensupplying a transmission signal to an electrode (that is, whentransmitting a signal), and grasps a state of capacitive coupling ofeach electrode on the basis of the signal level. Thus, the communicatingdevice 450 can simplify process steps, reduce a load, and also shorten aprocess performing time and thereby shorten the repetition period.

Incidentally, in the above description, the electrode controlling unit261, the electrode controlling unit 371, and the electrode controllingunit 451 each check states of capacitive coupling of respectiveelectrodes one by one. However, the present invention is not limited tothis; for example, states of capacitive coupling of all electrodes maybe checked simultaneously.

FIG. 19 is a block diagram showing an example of internal configurationof the electrode controlling unit 451 in the communicating device 450 inthis case. The electrode controlling unit 451 shown in FIG. 19 has adetecting unit 613 and a connecting unit 614 different from thedetecting unit and the connecting unit of the electrode controlling unit261 shown in FIG. 8.

The detecting unit 613 has a plurality of load resistances 621 to 624connected in series with each other between the switch 312 and areference point 626. Terminals 631A to 634A of the connecting unit 614are connected between the respective resistances (four points).Potentials of these connection points are each supplied to the retainingunit 303.

The resistance values of the load resistances 621 to 625 are each known.The terminals 631A to 634A of the connecting unit 614 are respectivelyone terminal of switches 631 to 634. When the switches 631 to 634 arebrought into an on state, the terminals 631A to 634A are respectivelyconnected to other terminals 631B to 634B. The terminals 631B to 634Bare respectively connected to the electrodes 461 to 464 of the electrodeunit 452.

Hence, for example, respective capacitances when the electrodes 461 to464 are each capacitively coupled with a space surrounding thecommunicating device 450 (when the communication medium is not in thevicinity) are known, and thus potentials between the load resistances621 to 624 when each switch of the connecting unit 614 is turned on arealso known.

When the communication medium is placed in proximity to an electrode, onthe other hand, the capacitance between the electrode and thesurroundings is changed. Thus, the detecting unit 613 detects resultingchanges in the potentials between the load resistances 621 to 624(changes in signal level), and makes the retaining unit 303 retain aresult of the detection. On the basis of the changes in the levels ofthe signals input to the respective electrodes which changes areretained in the retaining unit 303, the main control unit 301 controlsthe assignment of a function (the transmission signal electrode, thetransmission reference electrode, the received signal electrode, or thereception reference electrode) to each electrode.

Thus, since the states of capacitive coupling of the plurality ofelectrodes can be checked in one process, the communicating device 450can control the assignment of a function to each electrode more easilyand more quickly. Incidentally, any number of electrodes may be checkedsimultaneously at this time. All the electrodes possessed by thecommunicating device 450 may be checked simultaneously, or a part of theelectrodes possessed by the communicating device 450 may be checkedsimultaneously.

In addition, while in the above description, all the electrodes arechecked using one detecting unit, a plurality of detecting units may beprovided. For example, detecting units equal in number to that ofelectrodes may be provided, and the detecting units may be connected tothe electrodes different from each other. In this case, the detectingunits respectively detect signals input to the electrodes different fromeach other (each detecting unit detects a signal input to thecorresponding electrode).

As described above, the communicating device 450 to which the presentinvention is applied not only achieves a communication environment notlimited by a use environment by eliminating a need for a physicalreference point path and achieving communication by only a communicationsignal transmitting path, but also can perform stable communicationirrespective of positional relation between the communicating device 450and the communication medium in proximity to the communicating device450 by controlling the assignment of a function to each electrode.

Incidentally, in the above description, each device (the transmittingdevice, the receiving device, and the communicating device) in thecommunication system to which the present invention is applied transmitsor receives a signal with a predetermined potential as a reference.However, the present invention is not limited to this, and for exampletwo signals whose phases are reversed with respect to each other may betransmitted via two transmission lines, so that a differential signaltransmitting information represented by difference between the signalsis transmitted and received. In this case, the two transmission linesare provided as communication medium between the devices communicatingwith each other. Also, in this case, the transmitting unit in thetransmitting device, the receiving unit in the receiving device, and thecommunicating unit in the communicating device are each formed by adifferential circuit.

Incidentally, the series of processes described above (for example theelectrode controlling process and the like) can be carried out not onlyby hardware but also by software. In this case, for example, theabove-described main control unit 301 may be formed as a personalcomputer as shown in FIG. 20.

In FIG. 20, a CPU 701 of the personal computer 700 performs variousprocesses according to a program stored in a ROM 702 or a program loadedfrom a storage unit 713 into a RAM 703. The RAM 703 also stores data andthe like necessary for the CPU 701 to perform the various processes asrequired.

The CPU 701, the ROM 702, and the RAM 703 are interconnected via a bus704. The bus 704 is also connected with an input/output interface 710.

The input/output interface 710 is connected with an input unit 711formed by a keyboard, a mouse and the like, an output unit 712 includinga display formed by a CRT (Cathode Ray Tube), an LCD (Liquid CrystalDisplay) or the like, a speaker, and the like, the storage unit 713formed by a hard disk or the like, and a communication unit 714 formedby a modem or the like. The communication unit 714 performs a process ofcommunication via a network including the Internet. In addition, theoutput unit 712 is connected with the signal input controlling unit 302,the retaining unit 303, the connection controlling unit 304, theswitching controlling unit 305 and the like. The output unit 712 outputscontrol information to each of the units. Further, the input unit 711 isconnected with the retaining unit 303, so that information retained inthe retaining unit 303 is input from the retaining unit 303. Thisinformation is supplied to the CPU 701.

The input/output interface 710 is also connected with a drive 715 asrequired. A removable medium 721 such as a magnetic disk, an opticaldisk, a magneto-optical disk, a semiconductor memory or the like isloaded into the drive 715 as required. A computer program read from themedium is installed in the storage unit 713 as required.

When the above-described series of processes is to be carried out bysoftware, a program constituting the software is installed from anetwork or a recording medium.

As shown in FIG. 20, for example, the recording medium is not onlyformed by the removable medium 721 distributed to users to provide theprogram separately from the device proper and having the programrecorded thereon, the removable medium 721 including a magnetic disk(including flexible disks), an optical disk (including CD-ROM (CompactDisk-Read Only Memory) and DVD (Digital Versatile Disk)), amagneto-optical disk (including MD (Mini-Disk) (registered trademark)),a semiconductor memory or the like, but also formed by the ROM 702, thehard disk included in the storage unit 713, or the like that has theprogram recorded thereon and which is distributed to the user in a stateof being preincorporated in the device proper.

It is to be noted that in the present specification, the stepsdescribing the program recorded on the recording medium include not onlyprocesses carried out

1. A communicating device for performing communication via acommunication medium, said communicating device having a plurality ofelectrodes capacitively coupled with an outside, said communicatingdevice comprising: communication means for performing communicationprocessing means for performing communication processing; connectingmeans for connecting said communication processing means to saidplurality of electrodes; and connection controlling means forcontrolling said connecting means to connect a first electrode of saidplurality of electrodes, said first electrode being capacitively coupledwith said communication medium, to a first terminal of saidcommunication processing means, and connect a second electrodecapacitively coupled with a space more strongly than said firstelectrode to a second terminal of said communication processing means.2. The communicating device as claimed in claim 1, characterized inthat, said connection controlling means includes: signal level detectingmeans for detecting a signal level of a signal for checking a state ofcapacitive coupling of each of said plurality of electrodes withsurroundings when said signal is supplied to each electrode; andcontrolling means for controlling connection of said plurality ofelectrodes to said communication processing means on a basis of saidsignal level detected by said signal level detecting means.
 3. Thecommunicating device as claimed in claim 2, characterized in that: saidconnection controlling means further includes electrode selecting meansfor selecting an electrode to which to supply said signal, and saidsignal level detecting means detects the signal level of said signalwhen said signal is supplied to said electrode selected by saidelectrode selecting means.
 4. The communicating device as claimed inclaim 2, characterized in that: said connection controlling meansfurther includes retaining means for retaining said signal leveldetected by said signal level detecting means for each said electrode,and said controlling means controls the connection of said plurality ofelectrodes to said communication processing means on the basis of thesignal level of each said electrode, the signal level being retained bysaid retaining means.
 5. The communicating device as claimed in claim 2,characterized in that: said connection controlling means simultaneouslysupplies said signal to all said electrodes, and said signal leveldetecting means simultaneously detects said signal level correspondingto each of all the electrodes.
 6. The communicating device as claimed inclaim 4, characterized in that: said connection controlling meansfurther includes a plurality of loads connected to each of saidplurality of electrodes and connected in series with each other, andsaid signal level detecting means detects signal levels occurring atsaid plurality of loads connected in series with each other.
 7. Thecommunicating device as claimed in claim 1, characterized in that: saidconnection controlling means controls said connecting means afterstopping said communication processing by said communication processingmeans.
 8. The communicating device as claimed in claim 1, characterizedin that: said connection controlling means controls said connectingmeans in a free time of said communication processing by saidcommunication processing means.
 9. The communicating device as claimedin claim 1, characterized in that: said connection controlling meanscontrols said connecting means in a manner continuous with saidcommunication processing by said communication processing means.
 10. Thecommunicating device as claimed in claim 1, characterized in that: saidconnection controlling means controls said connecting meanssimultaneously with a transmission process by said communicationprocessing means, using a transmission signal in said transmissionprocess.
 11. The communicating device as claimed in claim 1,characterized in that: said communication processing means has atransmitting output terminal and a receiving input terminal, and saidconnection controlling means controls said connecting means to connectsaid first electrode to said transmitting output terminal or saidreceiving input terminal of said communication processing means.
 12. Acommunicating method of a communicating device for performingcommunication via a communication medium, said communicating devicehaving a plurality of electrodes capacitively coupled with an outside,said communicating method comprising: a communication controlling stepof controlling a communication processing unit for performingcommunication processing; and a connection controlling step ofcontrolling a connecting unit for connecting said communicationprocessing unit for performing said communication processing undercontrol of said communication controlling step to said plurality ofelectrodes to connect a first electrode of said plurality of electrodes,said first electrode being capacitively coupled with said communicationmedium, to a first terminal of said communication processing unit, andconnect a second electrode capacitively coupled with a space morestrongly than said first electrode to a second terminal of saidcommunication processing unit.
 13. A program for making a computerperform a process of a communicating device for performing communicationvia a communication medium, said communicating device having a pluralityof electrodes capacitively coupled with an outside, said programcomprising: a communication controlling step of controlling acommunication processing unit for performing communication processing;and a connection controlling step of controlling a connecting unit forconnecting said communication processing unit for performing saidcommunication processing under control of said communication controllingstep to said plurality of electrodes to connect a first electrode ofsaid plurality of electrodes, said first electrode being capacitivelycoupled with said communication medium, to a first terminal of saidcommunication processing unit, and connect a second electrodecapacitively coupled with a space more strongly than said firstelectrode to a second terminal of said communication processing unit.